It can be hard for parents and doctors to tell when those infections need treatment with antibiotics, and when they should be left to get better on their own.

The nation's pediatricians are trying to make that call a bit easier. In new guidelines released today, they say that it's OK to wait a while longer to see if a child gets better before treating a sinus infection with antibiotics. Now parents can wait and see what happens for 13 days instead of 10 days, the pediatricians recommend.

"There's nothing inviolate about 10 days," says Dr. Ellen Wald, chair of pediatrics at the University of Wisconsin who led the committee writing the new guidelines for the American Academy of Pediatrics. "If you want to give them another day or two to see if they get better on their own, that's perfectly reasonable."

The doctors are trying to balance the need to treat individual patients with the broader mission of reducing unnecessary prescriptions of antibiotics, which can promote resistance. "We're always anxious not to use antibiotics inappropriately," Wald tells Shots.

Children who are getting better but then get worse probably need antibiotics, Wald says, because that's a classic sign of a bacterial infection following a cold. Colds are caused by viruses. The guidelines were published in the journal Pediatrics.

A review in the same issue of Pediatrics found that antibiotics can help with children's sinus infections, but the researchers note that there's still only limited data. Just four studies that compared antibiotics to placebos have been done, and the results varied.

The use of antibiotics for sinus infections has been a point of controversy. A study last year in adults found that participants got better in 10 days, whether they got antibiotics or not.

One other key bit of new advice: Doctors shouldn't order X-rays or more elaborate scans for kids who may have sinusitis, the new guidelines say. That's because the swollen membranes of a cold look like sinusitus on an X-ray. "The inflammation that gives you that runny nose is not confined to your nasal membrane," Wald says.

But what about that green snot? That's not a reliable signal for a sinus infection, Wald says. "I think parents used to lean on that a lot." But it's more likely a sign that the snot has been in the nose overnight, not that there's necessarily anything nasty going on up there.

Some adults turn to surgery for recurring sinus infections, but doctors first recommend less invasive options, including rinsing the nasal passages with saline solution, and steroid nose sprays.